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FIGURE 11. DETAILS OF LARGE FLAT BAFFLE

4' BY 8' 1 " THICK PARTICLE BOARD

2 ' by 4 ' STIFFEN-
ERS MOUNTED AS
SHOWN ON BACK-
SIDE OF BAFFLES

PANELS BOLTED T O
EACH OTHER AND

T O 4508 ENCLO-
SURES, AS SHOWN.

16

FRONT VIEW

TOP VIEW

ADDED 2 BY 4

BRACES (AT 3
PLACES ON BACK

OF EACH BAFFLE)

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...
14
15
16
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18
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Summary of Contents for 4671

Page 1: ...ulticell designs of earlier years This manual is intended for both theater dealers and prospective purchasers of theater systems It will be use ful as a guide to the selection and installation of systems and it will provide considerable theoretical background for the specifying engineer 1 A Summary of House Types By far most of the theaters constructed today are relatively small rectangular rooms ...

Page 2: ...ow profile Alternate vented horn systems Models 4672A and 4674A Power needed for 100 dB 30 watts Characteristics Mid band sensitivity 103 dB one watt at one meter LF response limited due to horn load ing to be specified where available amplifier power is limited typically 50 watts or less C For theaters seating up to 500 patrons volume approximately 4500 cubic meters 160 000 cubic feet Preferred s...

Page 3: ... 4673 PMAX 150 W SENSITIVITY 97 dB 1 W 1 M 4670B PMAX 300 W SENSITIVITY 100 dB 1 W 1 M 4672A PMAX 150 W SENSITIVITY 103 dB 1 W 1 M 4674A PlVlAX 150 W SENSITIVITY 103 dB 1 W 1 M FIGURE 1B ON AXIS RESPONSE OF 4670B 2TT LOADING HIGH FREQUENCY POWER RESPONSE CORRECTED 3 dB Relative Response Frequency in Hz ...

Page 4: ...any dealers will want to take advantage of the fact that certain JBL theater low frequency systems are available loaded from the factory These are 4647 consisting of 4507 loaded with 2225H 4648 consisting of 4508 loaded with 2 2225H Further the 4671 OK is a factory preassembled ver sion of the utility system with an oak vinyl enclosure and brown grille cloth V3 SCREEN B Physical Considerations ABS...

Page 5: ...en the loudspeaker is placed on an elevated support it is advisable to anchor the loudspeaker with four or more angle irons so that it cannot possibly shift position The back wall behind the screen should be covered with a sound absorptive material 1 High frequency Horn Aiming Figure 3 shows details of mounting the components in the various systems Note that the high frequency horns are aimed stra...

Page 6: ...IN PLACE PANEL REMOVED B C 4 WOOD SCREWS INTO FRONT EDGES OF LF ENCLOSURE Use 1 0 x 2 flat head Philips wood screw pre drill holes with Va bit D MOUNTING LF TRANSDUCERS IN 4507 4508 AND 4518 E MOUNTING LF TRANSDUCERS IN 4550BKA AND 4560BKA ...

Page 7: ...FIGURE 3 Cont d H See note in text concerning polarity INCLUDED WITH NETWORK INSERT T NUTS 6 SCREWS TERMINAL BOARD PLATE REMOVED FROM INSIDE F G For 4671 4672A 4673 4674A For4670B 3115A 311 OA J 7 ...

Page 8: ...FIGURE 4 PROPER AIMING OF HIGH FREQUENCY HORNS A INVERSE SQUARE OFF AXIS TRADE OFF 0 Maximum output FIGURE 4B CADP DISPLAY HF HORN AIMED STRAIGHT AHEAD Screen HF Horn 10 high 12 2kHz 8 ...

Page 9: ...o do with the precise posi tioning of the high frequency driver with respect to the low frequency acoustic center There is one half wave length shift at the crossover frequency in these systems which requires the polarity change to maintain proper summation with the low frequency section Wiring from the projection booth to the screen loud speakers should conform to local codes The wire gauge selec...

Page 10: ... channel 300 watts into 4 ohms Characteristics Broad band sensitivity 100 dB SPL one watt at one meter JBL s most power flat and accurate system uses large Bi Radial horn for precise 90 by 40 degree pattern control down to 500 Hz integral power response correction extended response down to 45 Hz For very large houses and for the highest degree of performance in professional dubbing theaters and sc...

Page 11: ...PMAX 300 W SENSITIVITY 100 dB 1 W 1 M PMAX 300 W SENSITIVITY 100 dB 1 W 1 M PMAX 300 W SENSITIVITY 106 dB 1 W 1 M PMAX 300 W SENSITIVITY 109 dB 1 W 1 M FIGURE 6B ON AXIS RESPONSE 4675A 2ir LOADING HIGH FREQUENCY POWER RESPONSE CORRECTION ADDED dB Relative Response 11 Frequency in Hz ...

Page 12: ...cking capacitors in output of the high fre quency amplifier as shown in Figure 7C The capacitor protects the high frequency driver from any inadvertent DC or low frequency transients which could develop dur ing power up or power down phases of amplifier opera tion Figure 7D presents a table of capacitor sizes for various applications FIGURE 7 WIRING DIAGRAMS FOR LARGER SYSTEMS FIGURE 7A For 4675 a...

Page 13: ...CKING CAPACITOR FIGURE 7D BLOCKING CAPACITOR VALUES FOR DRIVER PROTECTION CAPACITOR JBL FOR OPTIMUM RESULTS VALUE PART AT THESE CROSSOVER NUMBER FREQUENCIES 36 JXF 62772 0360 500 Hz 24 jxF 62772 0240 800 Hz 1 6 0 OPERATION ASSUMED HF AMPLIFIER HF OUT LF AMPLIFIER BIAMPLIFICATION FIGURE 7B For 4676 B 2 Note Splay each HF horn 221 2 off center total splay is 45 ...

Page 14: ...s should be positioned about one third the way up the screen If the screen is flat as shown in Figure 9A the flanking loudspeakers should be toed in slightly Where the screen is curved as shown at B the loudspeakers may be positioned normal to the screen at each position The high frequency horns should be placed within 7 5 100 mm 3 to 4 in from the screen FIGURE 9 PLACING THE LOUDSPEAKERS BEHIND T...

Page 15: ...been specified for extra acoustical power output in the 40 Hz to 500 Hz range The baffle should not be interrupted and it should extend the entire width of the loudspeaker array Mechanical details of this baffle are given in Figure 11 Ideally the baffle should be continuous in a multi loud speaker screen array FIGURE 10 PHOTO OF ACADEMY OF MOTION PICTURE ARTS AND SCIENCES SYSTEM VIEW FROM ABOVE 15...

Page 16: ...AFFLE 4 BY 8 1 THICK PARTICLE BOARD 2 by 4 STIFFEN ERS MOUNTED AS SHOWN ON BACK SIDE OF BAFFLES PANELS BOLTED TO EACH OTHER AND TO 4508 ENCLO SURES AS SHOWN 16 FRONT VIEW TOP VIEW ADDED 2 BY 4 BRACES AT 3 PLACES ON BACK OF EACH BAFFLE ...

Page 17: ...lated to system efficiency 2 Choosing the right surround loudspeakers JBL has recently introduced the model 8325A three way system for surround applications With input power capacity of 80 watts and a sensitivity of 91 dB one watt at one meter ten to twelve of these systems are a rea sonable match for a screen array of 4675A systems More than ten may be required for broader coverage in larger hous...

Page 18: ...low frequency effects in the motion picture theater date back to the thirties but the present interest dates from Universal s Sensurround in the seventies Since that time special low frequency channels for cov ering the range from 20 to 40 Hz have become common in large theaters and the Dolby CP200 processing unit has a summed output below 100 Hz that can be used di rectly for driving subwoofer am...

Page 19: ... of transducers the maximum sound pressure level increases 6 dB Three dB are due to doubling the power Subwoofer loudspeakers should be located fairly close together and they should be placed at the inter section of a wall and floor Careful bracing and mounting on rubber or Neoprene pads may be necessary to mini mize rattling FIGURE 14B ROBINSON DADSON EQUAL LOUDNESS CONTOURS F Acoustical Response...

Page 20: ... B and typical high frequency screen losses are shown at C When we add all of these losses we get the response shown at D and this is exactly the acoustical response we would observe in the room if we were using a loud speaker that had flat power response FIGURE 15 RESPONSE IN THE HOUSE ROOM BOUNDARY LOSSES EXPRESSED IN dB TYPICAL AIR LOSSES AT 15 METERS 50 RELATIVE HUMIDITY SUM OF CURVES A B AND ...

Page 21: ... normal power response roll off of the compression driver JBL recommends that the boost be used in all theater systems The model 3152A network has been replaced by the 3160 There are two important differences between the old and new models The impedance of the low fre quency section has been changed from eight to four ohms thus providing a better sensitivity match between the low and high sections...

Page 22: ...e controls on amplifiers will discourage tampering The JBL models 6230 6260 and 6290 amplifiers are available with such controls 2 An experienced technician should regularly check out each audio chain to ensure that no changes have been made 3 Make sure that any changes in third octave sys tem equalization are carried out by an experienced engi neer using the correct measuring instrumentation 4 Th...

Page 23: ...ow Frequency Enclosure 1 2225H Low Frequency Transducer 1 2380 High Frequency Horn 1 2445J High Frequency Driver 1 3115A Network F 4675A 1 4508 Low Frequency Enclosure 2 2225H Low Frequency Transducers 1 2360A High Frequency Horn 1 2445J High Frequency Driver 1 2506 Mounting Bracket 1 3160 Network a 4675A 2 2 4508 BKA Low Frequency Enclosures 4 2225J Low Frequency Transducers 1 2360A High Frequenc...

Page 24: ...JBL Professional 8500 Balboa Boulevard P O Box 2200 Northridge California 91329 U S A ...

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